A single query can be run using various methods or rewritten in various formats and STRUCTURES. As a result, the topic of query optimization arises: which of these forms or paths is the most efficient? The query optimizer considers all alternative query plans to discover the most efficient way to EXECUTE a query.

The purpose of query optimization is to reduce the number of system resources necessary to complete a query, allowing the user to receive the proper result set more quickly.

• It gives the user faster results, making the application appear to be speedier.
• Second, because each request takes less time than unoptimized queries, the system can HANDLE more queries in the same amount of time.
• Finally, query optimization decreases the amount of WEAR on the server's hardware (for example, disk drives) and allows it to run more efficiently (e.g. lower power consumption, less memory usage).

A query can be optimised in one of two ways: 

• Analyze and alter RELATIONAL phrases that are equivalent: Reduce the number of tuples and columns in the intermediate and final query processes (discussed here).
• For each operation, multiple algorithms can be used: These underlying techniques influence the frequency of disk and block accesses by determining how tuples are accessed from the data structures they are stored in, indexing, hashing, and data retrieval.